Floor-mounted powered cargo systems are used to facilitate movement of cargo containers inside the main deck and lower lobe compartments of wide-bodied aircraft. While movement of cargo inside an aircraft has traditionally been done by hand, the development of large and heavy cargo containers necessitates the use of a powered cargo system. One prior cargo system uses a plurality of pneumatic rollers, each roller being powered by an individual motor. The roller and motor unit is pivotally mounted in a floor recess. A disadvantage of this prior system is that the pneumatic rollers tend to lose air and go flat. Another disadvantage of this system is that the limited vertical floor space in an aircraft restricts the diameter of the roller. As a result, the tractional bearing area of each roller is so small that for heavy containers or containers having slick bottom surfaces manual help is required to move them in the compartment. Furthermore, because of the recessed floor mounting, any repositioning of the units requires structural modification of the floor.
One proposal for overcoming the disadvantages associated with this prior system suggests using a solid roller in place of the pneumatic roller. This proposal has the drawback of increasing the weight of the cargo system. Another proposed design replaces the pneumatic roller with a plurality of small diameter, solid rollers driven by a single motor. While this design successfully increases tractional bearing area and decreases the weight borne by a single roller, it has proved unsuitable for aircraft cargo systems because it does not permit automatic or manual engagement and disengagement of the rollers with the drive motor. This drawback prevents loading or unloading of the cargo compartments should electric power not be available. This drawback also prevents selective movement of individual cargo containers that simultaneously overlap one or more sets of rollers with another cargo container. Finally, this system has no means for limiting the amount of torque that can be applied to the roller drive train to avoid damage in overload conditions.